Resposta da capacidade de sorção de fósforo do solo a ocupação urbana em ecossistemas tropicais

Abstract

Phosphorus (P) is naturally present in soils. Changes in land use can promote additional inputs of P into the soil that lead to saturation of binding sites exceeding the maximum sorption capacity of P in the soil. Besides P input, urban occupation promotes changes in soil attributes that contribute to intensify soil vulnerability to erosion and P flux from soil to aquatic ecosystems, aggravating the water crisis, especially in the semiarid region. The objective of this study was to evaluate the sorption characteristics of P in urban soils and to verify their relationship with soil attributes. A total of fifty soil samples, twenty-five of natural and twenty-five of urban soils were selected from different watersheds in the state. The soil samples were characterized physically and chemically. The P sorption characteristics were obtained by fitting the Langmuir and Freundlich equations. Descriptive statistics, Pearson correlation and Principal Component Analysis (PCA) were used to analyze these data. Urban soils showed lower P sorption capacity. The increase of P-rem, pH, available P and reduction of clay contents occurred concomitantly with the increase of phosphorus saturation index and the reduction of soil P sorption capacity in urban soils, being good indicators of P source soils in watersheds. Lower Smáx, clay content and Freundlich constant 1/n best distinguished natural from urban soils regarding P sorption. The results show the reduction of P sorption capacity in soils, increasing its mobility in watersheds and the risks related to P loads in aquatic ecosystems with urban expansion worldwide. These data serve as a basis for decision making regarding the appropriate management of soils in urban expansion areas in watersheds in order to control the flux of P to aquatic systems.